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Commercial Kitchen Vent/HVAC issue

Inspected a local brew pub with some unusal HVAC/venting issues that I would be interested in a professional opinion on.

On humid days (and only during hot humid days) they have some water leaking from ducts and venting equipment. The worst location is the basement kitchen (huge commercial set up with 4 cooktops, 2 fryers, etc). Although I did not observe it, I am told that so much water was dripping from the vents that they had to rig up a makeshift gutter to run the water to the sink. It seems logical to me that since it only occurs on days when teh exterior air is humid that the issue must be related to the make up air system (a huge commecrial unit on the 5th story roof) but I am seeking professional thoughts on that..... There were some small (4 square inches) holes in teh duct work running from the intake unit on the roof down to the kitchen, but these did not seem large enough to account fo rthe mass quantities of water the manager decribes.

Other locations of dripping: The HVAC vent at the top of the stairs (possibly condensation from teh heat of the kitchen rising up?); A bathroom HVAC vent (located pretty far from all other concerns, but adjacent to the exterior brick wall and in a fairly isolated section of a large restaurant bathroom with 15 foot ceilings); and two exposed metal HVAC ducts at the front entry (possibly from entry air mixing with the greenhouse effect of the enormous picture windows).

Any thoughts? Incidentally they have had 3 contractors out to look at the HVAC system (not the kitchen venting and make up air, though, for some reason) and they could not identify the problem. Also, the brew room is totally sealed off from teh rest of the place with its own HVAC systems.

I welcome your input as I would like to offer some suggestions for the frustrated owners.....

What is the discharge air temp? If too cold the ductwork insulation will be inadequate. Several things might cause a drop in the DA temp. Dirty coils, dirty filters, worn sheaves, all will lower air flow causing the discharge air temp to drop. I'ld bet one of the above, but it could be someone has made changes and caused the problem by trying to get more cooling.

Good questions - I don't have the answers to all....but here are some ballpark answers which may help you.

Average indoor temp is a steady 70 (that's what they have it set at) for the restaurant area. The kitchen is WAY hotter than that (it was over 90 on a 60 degree day) and even hotter over teh cooktops (where the major problem exists).

Duct work is only partially exposed (the exposed parts are metal) while most seems insulated (does not appear metal, but I only got a limited look through some registers).

Air infiltration is likely (since this only occurs when it is humid out - as opposed to hot but not humid), but only through the front doors (when customers come in) or through the make up air duct (insulated, not metal BTW).

What is the discharge air temp? If too cold the ductwork insulation will be inadequate. Several things might cause a drop in the DA temp. Dirty coils, dirty filters, worn sheaves, all will lower air flow causing the discharge air temp to drop. I'ld bet one of the above, but it could be someone has made changes and caused the problem by trying to get more cooling.

If the space humidity is abnormally high that would contribute too.

Thanks, Bob.

I think those things have been checked, and they may be responsible for the upper restaurant issues (I think teh heat and humidity from teh kitchen contributes to condenastion at one register, while the huge picture windows and entering customers may contribute to teh other problem). I will have to recommend cleaning of the items you suggested and a primer course for employees on humidity and cooling systems ("don't touch the freaking thermostat!")

How would that all apply to the waterfall (indoor rain seems accurate from their description) at the hood vent? I can see that high temps exist there, but it would seem that the humidity should be sucked out, not condensing there.... And the fact taht it only is noted when it is humid out keeps me wondering about any role the make up air plays in this (since I can't see how else any humid air is getting from outside into a basement kitchen.)

If they condition the make up air to the kitchen Ive seen this done the air is dumped at the front edge of the hood this cold air below dewpoint is hitting sufrace causing zone where humid air in kitchen condenses ..... I see this in the winter here when the restaurant doesnt want to heat the fresh make up air the cool outdoor air is causing same situation..... good luck

If they condition the make up air to the kitchen Ive seen this done the air is dumped at the front edge of the hood this cold air below dewpoint is hitting sufrace causing zone where humid air in kitchen condenses ..... I see this in the winter here when the restaurant doesnt want to heat the fresh make up air the cool outdoor air is causing same situation..... good luck

Sounds like what I was thinking. I think the warm humid, summer air is being cooled and not adequately dehumidified before getting dumped near the hot hood vent (but I am a novice with commerial systems like this). Hope that made sense....

yes it only has one pass over coil and has very little humidity taken out... nopt many kitchens here condition make up air ,,, the cooks are all sweating buckets....wherever the cool air is hitting it is causing cold spot causing condensation then dripping.....you could maybe dump fresh air through ceiling vents let air pass over cooks then up hood this would end condensation...insulate the fresh air pipe in ceiling....I cant recall if there are rules about where the make up air is dropped... I know alot of hood manufacturers want it dumped in chnnel at hood lip for containment of smoke,,, Ive dumped some air in kitchen and you have to be careful of air streams disrupting exhaust hood area... good luck...

is there a fire damper closed in the duct work?
Is the condensate comming fron the inside or the outside of the duct?you said a 5 story building,does it rise 5 stories to exhaust?Is FAN TURNING IN THE RIGHT DIRECTION AND MOVING ENOUGHT AIR?has it always done this?or a new problem?

I think you need to look at the vent hood itself, The water should be draining out of the top with the grease from the catch pan on the roof. Im sure the vent cap needs cleaned out, they fill up with oil and dirt pretty quick. The same is true for the AC. Start with a good cleaning. kitchens need the the equipment cleaned on a regular basis. Its a nasty job but needs to be done so that everything will work properly